This invention relates to gas-treatment devices.
The invention is more particularly concerned with heat and moisture exchangers (HMEs) or the like for use with tracheostomy tubes.
In normal breathing, inhaled air passes through the nose where it is warmed and moistened before passing to the trachea and bronchial passages. Where a patient breathes via a tracheal tube or laryngeal mask, gas is supplied directly to the trachea, by-passing the nose. The gas is, therefore, preferably warmed and moistened to prevent discomfort and damage to the lining of the trachea. This is often achieved by a heat and moisture exchange device or HME connected to the tracheal tube to receive both exhaled and inhaled gases. The HME has a moisture-absorbing element, such as of a treated paper or foam, that absorbs moisture in exhaled gases and transfers a major part of this to the inhaled gases. The element also warms inhaled gas in the same way. HMEs are sold by Portex Limited of Hythe, England under the trade mark Thermovent. Examples of HMEs are described in: GB 2303307; GB 2321600; GB 2277689; GB 2268496; GB2267840; GB 2233904; EP 535016; EP 533644; EP 387220; EP 265163; EP 413127; U.S. Pat. No. 4,516,573; U.S. Pat. No. 4,090,513; U.S. Pat. No. 4,771,770; U.S. Pat. No. 4,200,094; and U.S. Pat. No. 4,048,993. The HME may also include a filter for removing particles, bacteria and viruses from gas supplied to or from the patient.
Conventional HMEs have an exchange element within a rigid housing that is coupled to the machine end of the tracheal tube. This can be relatively bulky and is a particular problem where the patient is breathing unaided via a tracheostomy tube since it is preferable for this to be as unobtrusive as possible.